Feeders that selectively deliver articles to a work zone in a manufacturing operation are well known. For example, in the packaging industry, the packaging of food or beverage containers, such as bottles or cans, into cartons requires high speed feeders that deliver carton blanks successively to a conveyor, which then delivers the blanks to the next work station. The carton blanks generally are substantially flat, stiff paperboard or corrugated board items that previously have been fabricated from rolled stock by cutting blanks from the stock and scoring features, such as fold lines and score lines, into the blanks. Similar feeders also are employed in many other industries, such as in the magazine and publications industries, where the continuous sequential feeding of relatively flat articles from a stack or queue is required. U.S. Pat. No. 6,550,608, owned by the assignee of the present application, discloses a carton feeding system for a packaging machine that exemplifies many of the attributes mentioned above. This patent is hereby incorporated by reference in its entirety.
The term “carton feeder” commonly is used to refer to feeders that select and deliver carton blanks to a work zone in high speed continuous packaging operations. Many different types of carton feeders are used in the packaging industry, and have varying features depending upon the specific use and application requirements. It is common, however, for carton feeders to include some common structural and operation features. For example, most carton feeders used in the packaging industry are part of a carton feeding system, which can include a device for delivering stacks of carton blanks to a carton magazine. The carton magazine stores sufficient numbers of carton blanks and includes a conveyor system for conveying the blanks toward the feeder. At the feeder, individual carton blanks are sequentially selected or picked from the forwardmost end of the stack and delivered to downstream workstations of the packaging machine.
A carton magazine typically supports carton blanks on edge in a horizontal stack of hundreds or thousands of blanks, so that each carton blank rests on an edge with one face of the blank generally facing in a downstream direction toward the feeder. The magazine can include a conveyor, such as moving chain flights, on which the stack of blanks rests, and which progressively moves the carton blanks toward the feeder as the feeder progressively picks carton blanks from the forwardmost end of the stack. Rails on either side of the conveyor may maintain the stack of blanks centered or otherwise properly positioned on the conveyor. The stack of carton blanks generally is tilted, at least in the vicinity of the feeder, slightly towards the feeder to insure that the blanks maintain their upright orientations.
At a selection zone of the carton feeder, which is disposed at the most downstream end or position of the magazine, the first exposed carton in the stack contacts and is supported along its top edge by, for example, a bar or a shaft having rollers or by mechanical clips or tabs. This top edge leans against the rollers of the shaft, or against the bar or clips, depending upon the elements used, to support the upper edge portion of the stack of blanks. The bottom edge of the forwardmost blank in the magazine also contacts and is held by mechanical elements such as upstanding clips or tabs. The exposed forwardmost blank in the stack, and the stack itself, is thus supported in the proper position for selection of the forwardmost blank by the feeder. In this position, the forwardmost carton blank in the stack is urged with significant force against the rollers, bar, or clips, either by the weight of the stack of blanks, or by the force of the conveyor moving the stack forward, or both.
In one feeder system, a long horizontally oriented section of the magazine, which may support and convey thousands of carton blanks, terminates at a short downwardly oriented chute section of the magazine, sometimes referred to as the waterfall. Shorter stacks of carton blanks are conveyed from the horizontally oriented portion of the magazine into the chute, where they come to rest against the aforementioned shaft, clips, and/or tabs with the exposed face of the forwardmost blank always exposed so that it may be selected from the stack.
A common selection mechanism for a carton feeder is a vacuum system. This system includes a group of spaced vacuum cups on a pick arm assembly that are controlled to move into engagement with the exposed face of the forwardmost blank in the magazine, attach with a vacuum seal, pull the forwardmost blank from the stack, and slide the blank off of the stack for delivery to downstream stations of the packaging machine. The vacuum system includes vacuum lines, valves, and pumps that are operated in timed relationship, so that a vacuum is drawn on the face of the blank at the desired moment and held until the carton blank is released by the vacuum system. Once the forwardmost carton blank is contacted by the vacuum cups, the pick arm assembly pulls the carton blank forwardly away from the magazine a short distance until one edge of the carton blank is pulled over and away from contact with the clips or tabs holding the edge in position. The pick arm assembly then may be rotated, or otherwise moved, to slide the selected blank from beneath the shaft, clips, and/or tabs at the other edge of the blank and off of the end of the stack. The selected blank is then moved to the next work station, usually a conveyor assembly. At this position, the carton blank is released by the vacuum system and the carton is moved by the conveyor to the next area, where the carton either is folded around a group of containers, or erected, or positioned over a group of containers, depending upon the type of carton blank used. The pick arm assembly may include a plurality of vacuum cup assemblies that select carton blanks from the stack in rapid succession.
Selection and removal of the single forwardmost or first carton blank from the magazine requires that the vacuum cup attachment and forces applied to pull the carton blank forward and then slide it from beneath the clips and off of the stack are sufficient to overcome the mechanical forces that hold the carton blank in the magazine. Usually these forces include friction that is induced by the weight of the carton stack and/or the magazine chain conveyor pressing the forwardmost carton against the rollers and/or clips at the end of the magazine. If the vacuum is insufficient or the pulling forces are insufficient to overcome this friction, the carton blank will not be selected correctly. For The force of the vacuum attaching the vacuum cups to the face of the forwardmost carton is strongest in a direction perpendicular to the face of the blank; that is, along the axis of the vacuum cup. Conversely, the force is weakest in a direction parallel to the face of the blank or transverse to the axis of the vacuum cup. As a consequence, one edge of the forwardmost blank often is pulled easily over and away from the clips holding it in place at the end of the magazine. However, when the pick arm assembly rotates the vacuum cups to slide the blank off of the stack, the friction between the blank and the bar and/or clips holding the opposite edge portion of the blank can be sufficiently great to overcome the force of the vacuum. This can cause the vacuum cups to slide or slip off the face of the blank, particularly during high speed operation of the feeder. The result can be that a carton blank is not picked, or selected, from the magazine, or that a carton blank is only partially separated from the magazine, resulting in a system jamb and an operational stoppage.
Therefore, there is an advantage in reducing the frictional forces that are exerted on the forwardmost carton blank in a magazine in these types of feeder systems, so that the gripping force of the vacuum cups needed to select the first carton reliably also is reduced and/or controlled. Prior feeder systems have addressed this issue by using small spaced clips instead of bars at the end of the magazine to hold the forwardmost carton blank at its edges, thus reducing the contact area between the carton edge and the mechanical element. Other methods and elements used to reduce the frictional forces between carton blanks and the mechanical structures holding them in place at the end of the magazine include freewheeling rollers placed along a support shaft instead of clips or bars. Sometimes the rollers themselves can be positively driven by a shaft, in order to reduce further the force needed to select the first carton. Another prior feeder system includes a movable support bar synchronized with the pick arm and suction cups such that just before a blank is to be slid off the stack at the end of the magazine, the support bar moves quickly a short distance toward the stack of blanks and back again to toss the stack briefly backward a short distance. The forwardmost blank is then slid from beneath the support bar as the stack falls back toward the support bar, a time when friction allegedly is reduced.
A need exists for an improved system for insuring that the forwardmost carton blank of a stack in the magazine is reliably selected and removed from the stack, particularly during high speed operation of the packaging machine. It is to the provision of such a system that the present invention is primarily directed.